This invention relates to a magnetic pickup sensor and, more particularly, to a magnetic pickup sensor in which a magnet-and-coil sensor assembly is disposed within a molded resin housing.
FIGS. 4 and 5 illustrate a known magnetic pickup sensor particularly useful when used for generating an ignition timing signal in internal combustion engines. The illustrated magnetic pickup sensor comprises a sensor assembly 1 and a molded resin housing 2 having a mounting flange 2a disposed around the sensor assembly 1 and defining an outer housing for the sensor assembly 1.
The sensor assembly 1 comprises a substantially disc-shaped permanent magnet 3 as shown in FIG. 5, a magnetic iron core 4 coaxially aligned with the permanent magnet 3 for defining a magnetic path for allowing the passage of the magnetic flux generated from the magnet 3 and a pickup coil 5 wound around the iron core 4 for detecting a change in magnetic flux passing through the iron core 4. The sensor assembly 1 also comprises a support unit 6 for supporting the permanent magnet 3, the iron core 4 and the pickup coil 5 into an assembled state. The sensor assembly 1 has connected thereto an output wire 7.
The support unit 6 comprises a coil bobbin 8 disposed around the iron core 4 and around which the sensor coil 5 is wound, a sleeve 9 attached to the coil bobbin 8 for holding the magnet 3 in magnetic coupling relationship relative to the iron core 4 and a spacer 10 inserted within the sleeve 9 for holding the magnet 3 within the sleeve 9.
During the manufacture of the magnetic pickup sensor, in order to form the molded resin housing 2 around the sensor assembly 1, the sensor assembly 1 must be placed within a mold cavity defined by a mold die as is readily apparent from FIG. 4. In positioning the sensor assembly 1 within the mold cavity, one end 4a of the magnetic iron core 4 which projects from the assembly 1 and from the mold resin housing 2 is positioned within a recess formed in a cavity wall surface so that the projecting end 4a of the iron core 4 is accurately positioned in the mold resin housing 2.
However, as easily understood from FIG. 4, since the sensor assembly 1 is positioned and supported within the mold cavity only at one end of the assembly 1 or the projecting end 4a of the iron core 4, the position of the sensor assembly 1 within the mold cavity is not completely stable and the sensor assembly 1 can quite easily tilt from its correct position with respect to the molded resin housing 2. The output wire 7 connected to the sensor assembly 1 may provide some support for the assembly 1, but the flexibility of the output wire 7 and the position at which the wire 7 is connected to the assembly 1 make the support during the molding procedure insufficient. When the sensor assembly 1 tilts and is moved out of the correct position within the molded resin housing 2, the positional accuracy of the iron core 4 cannot be maintained, which may cause the inaccuracy of the measurement of the sensor assembly 1. When the sensor assembly 1 is tilted and out of correct position within the molded resin housing 2 in the completed magnetic pickup sensor, the measurement accuracy of the sensor assembly 1 is degraded when the molded resin housing 2 is installed relative to the object to be detected by means of a mounting flange 2a.